It is known to construct both dielectric and double layer capacitors in accordance with the following general steps. Initially, a pair of foil electrodes, with an appropriate intermediate dielectric or separator, as the case may be, are overlapped and wound together into a spiral configuration to define a cylindrical body. The nature of the overlap is such that the electrodes protrude from respective opposed axial ends of the body. For dielectric capacitors it is known from U.S. Pat. No. 1,479,315 to form a metallised layer on the two ends of the body and from U.S. Pat. No. 3,256,472 to subsequently solder lead wires, or terminals, to those layers. Insofar as double layer capacitors and other electrochemical cells are concerned the use of metallisation layers and soldering has not been effective due to corrosion problems arising from the use of an electrolyte within such cells.
Accordingly, for double layer capacitors the terminals are usually connected to the respective electrodes by "stakinge" or spot welding. While these operations have the advantage of simplicity and low cost they are also known to distort the shape of the electrodes and thereby compromise the quality and longevity of the capacitor. Additionally, the resultant electrical connection between the terminals and electrodes often have a high electrical resistance, thereby increasing the overall series resistance of the capacitor.
An alternative approach for double layer capacitors is to utilise a non-porous metallisation layer. In practical terms, however, this is unworkable, as the ingress of the electrolyte into the capacitor is slowed prohibitively.
The prior art also suffers from the limitations of forming a metallisation layer. More particularly, during metallisation it is known that some of the particles being applied will enter between the spaced apart portions of the electrode. If the number of such particles is sufficient they short circuit the two electrodes and either reduce the overall capacitance or render the capacitor defective. A partial solution to this problem is to reducing the overlap of the sheets so that the particles will have to travel further before contacting the other electrode. This, however, reduces the capacitance and increases the bulk of the resultant capacitor.